1. Technical Field of the Invention
The present invention relates to a spindle apparatus of a machine tool or more particularly to a spindle apparatus equipped with a control apparatus for preventing seizure.
2. Prior Art
When a spindle apparatus of a fixed position and pressurized type supported by rolling bearings is operated at a rotational speed higher than 1 million d.sub.m n [d.sub.m n signifies the product of the diametral pitch of rolling elements d.sub.m (mm) and the rotational speed (rpm)], the clearance in the bearings may be reduced due to expansion of the inner race of the bearing, the temperature difference between the inner race and the outer race and the like. As a result, the prestress of the bearing will be increased causing seizure when the conditions of supplying lubricants and cooling the bearings cannot comply with said increase in prestress. Method used to eliminate this problem, consist mainly of measuring the temperature of the housing and predicting the possibility of seizure in accordance with the result of said measurement and a method of predicting possible seizure by used of acoustic emission (AE).
However, there have been problems in that the response to prediction of seizure based on the measurement of the temperature of the housing was so delayed that seizure might have happened by the time such seizure prediction data was detected, thus making prevention of seizure not reliable. Particularly recently, since the housing is cooled by means of a jacket, the above-mentioned method based on temperature detection has been made difficult. Also the method of predicting seizure by use of acoustic emission (AE) has been made difficult in the case where a housing is cooled by means of a jacket because a sensor is provided with a housing and detects the states thereof. There is still another problem in that the method of predicting seizure by use of acoustic emission (AE) is as yet unreliable for practical use.